1. Field of the Invention
The present invention relates to a fixing liquid for fixing microparticles containing a resin to a medium, a fixing device using this fixing liquid, and an image forming apparatus comprising this fixing device.
2. Description of the Related Art
Image forming apparatuses such as a printer, a facsimile machine, and a copying machine are apparatuses for forming an image, which may include characters and/or symbols, on a recording medium such as paper, cloth, and an OHP sheet, based on image information. Particularly, electrophotographic image forming apparatuses have been widely used in offices since a high-definition image can be formed on a normal paper with high speed. In such an electrophotographic image forming apparatus, a heat fixing method has been widely used in which toner is fixed on a recording medium by heating or fusing the toner on the recording medium and by pressing the fused toner. This heat-fixing method has been preferably used since a high fixing speed, a high fixed image quality, and the like can be provided.
However, approximately half or more of electric power consumed in such an electrophotographic image forming apparatus is consumed for heating toner in the heat fixing method. On the other hand, a fixing device with low electric power consumption (intended for energy conservation) is desired from the viewpoint of recent measures against environmental problems. That is, a fixing method is desired which does not require to extremely lower the temperature at which toner is heated, compared to a conventional case, or to heat toner, with a view of fixing the toner. Particularly, a non-heat fixing method of fixing toner on a recording medium, in which toner is not heated at all, is ideal as regards low electric power consumption.
As such no-heat fixing method, for example, Japanese Patent No. 3290513 (Prior Art 1) discloses a method for wet-fixing toner which includes spraying or dropping an oil-drop-in-water-type fixing agent, in which an organic compound capable of dissolving or swelling toner and insoluble or hardly soluble in water is dispersed and mixed in water, onto a surface of an object to be subjected to fixing and on which unfixed toner is disposed at a predetermined position, followed by drying the object subjected to fixing.
Since the wet-fixing method disclosed in the Prior Art 1 uses an oil-drop-in-water-type fixing agent in which an organic compound insoluble or hardly soluble in water is dispersed and mixed in water, however, when a large quantity of the fixing agent is provided to unfixed toner, a recording medium (an object to be subjected to fixing) such as transfer paper or the like absorbs water of the fixing agent, whereupon wrinkles and/or curls form on the recording medium. Accordingly, this impairs remarkably the stability and high speed of conveyance of the recording medium required by the image forming apparatus. Then, where a large quantity of water contained in the fixing agent is evaporated using a dryer so as to remove the water content from the fixing agent provided on a the recording medium, electric power is needed which corresponds to the electric power consumed in an image forming apparatus using the heat-fixing method.
Also, usually, the surface of toner particles is water-repellency treated with hydrophobic silica or the like, in order to prevent the toner particles from absorbing atmospheric moisture and from aggregating with one another, and to preserve the fluidity of the toner. Therefore, when an aqueous fixing liquid containing water as a dispersion medium, as the aforementioned fixing agent, is sprayed or dropped onto unfixed toner on a recording medium, the water-repellency treated toner particles are repelled by the aqueous fixing liquid. As a result, a blank portion is formed on a toner image and a defect is produced on the image. The aqueous fixing liquid is also prone to suffer the drawback of a changing component ratio in the fixing liquid as a result of water, as a diluted solvent, evaporating inside the image forming apparatus.
Herein, there is also disclosed, as a fixing liquid which does not repel water-repellency treated unfixed toner, an oil based fixing liquid in which a material capable of dissolving or swelling toner is dissolved in an oil based solvent. For example, Japanese Unexamined Patent Application Laid-open No. 2004-109749 (Prior Art 2) discloses a fixing liquid in which an ester from an aliphatic dibasic acid or the like, as a material component capable of dissolving or swelling a resin component that makes up a toner, is diluted with (or dissolved in) nonvolatile dimethyl silicone as a diluent (or solvent).
Also, Japanese Unexamined Patent Application Laid-open No. S59-119364 (Prior Art 3) discloses a fixing solution for fixing an unfixed toner image, the fixing solution dissolving the toner and being in a phase solution state resulting from mixing 8 to 120 parts by volume of a silicone oil into 100 parts by volume of a solvent having compatibility with the silicone oil, as a fixing solution that can be used in a fixing method that allows fixing an unfixed image, formed by an electrostatic method, on an image receiving sheet, easily and without disturbing the image. Since such an oil based fixing liquid contains an oil based solvent having a high affinity with water-repellency treated unfixed toner, the toner can be dissolved or swelled and fixed on a recording medium without repelling the water-repellency treated unfixed toner.
Herein, the use of a VOC (volatile organic compound) as an oil based solvent used for an oil based fixing liquid has an adverse affect on the human body, causes the generation of unpleasant odor and, therefore, is not preferable. Consequently, a nonvolatile oil based solvent is practically used as an oil based solvent employed in an oil based fixing liquid.
However, an oil based fixing liquid in which a material capable of dissolving or swelling toner is dissolved in a nonvolatile oil based solvent has a high permeability into a recording medium. Therefore, when an oil based fixing liquid as described above is sprayed or dropped onto unfixed toner on a recording medium, the oil based fixing liquid has a high speed of diffusion and/or penetration into and through the recording medium, and only a portion of the material capable of dissolving or swelling toner contained in the oil based fixing liquid dissolves or swells the unfixed toner on the recording medium. Thus, the residual portion of the material capable of dissolving or swelling toner is not utilized for dissolving or swelling the toner and diffuses into the recording medium, or passes through the recording medium, together with the oil based solvent.
Since only a portion of the material capable of dissolving or swelling toner contained in the oil based fixing liquid dissolves or swells the unfixed toner on the recording medium, it becomes necessary to increase, in the oil based fixing liquid, the concentration of the contained material capable of dissolving or swelling toner. For example, the concentration of a solvent dissolved into a silicone oil as an oil based solvent in the fixing solution disclosed in the Prior Art 3 must be at least 20 wt %. This results in low toner dissolving or swelling efficiency in an oil based fixing liquid where the material that dissolves or swells the toner is dissolved in a nonvolatile oil based solvent.